User:Uzoma Anele

Uzoma Anele, Sandeep Pulugurtha Undergraduate students at the University of Maryland, Baltimore County.

Helical Thong of Glutamine Synthetase
Helical thong complexes, represented here by space-filling models, are interactions that bind together subunits from the two hexameric rings of glutamine synthetase. There exist 12 helical thongs in glutamine synthetase, each extending from each subunit. A helical thong, shown here in red, is composed of a nonpolar carboxyl terminus (in this case of subunit A) that inserts into a hydrophobic pocket created by two adjoining subunits (in this case subunits G and L) on the opposite, corresponding layer. An example of the helical thong complex details the C-terminal helix in red inserted into the hydrophobic pocket. Thirty-seven of the 77 residues of which the helical thong and hydrophobic pocket consist, are apolar (shown in gray) and are involved in the direct contact between the helical thong and pocket. Approximations of the stabilizing free eneregy created by these hydrophobic interactions suggest that helical thongs rely much more on hydrophobic interactions than hydrogen bonds. These residues contain an atypical abundance of proline and valine, 16% and 10%, respectively (with proline shown in pink and valine in green). This unusual amount of proline and valine is thought to help contribute to the enzyme's rigidity and cohesion. Helical thongs provide a significant amount of intersubunit stabilization to the quaternary structure of glutamine synthetase.



=References= 1. Eisenberg, D., et.al., Structure-function relationships of glutamine synthetases, Biochim Biophys Acta 2000: 1477, 122-145.

2. Yamashita, M. M., et.al., Refined Atolnic Model of Glutamine Synthetase at 3.5 A Resolution, J Biol Chem 1989 264: 17681-17690.